Many types of autoinjector devices exist for providing an automatic means for delivering a dose of medicament. An example of a known autoinjector device is described in the applicant's granted European Patent EP-B-1715903 (The Medical House plc).
Many autoinjectors described in the prior art comprise an energy source such as a spring or compressed gas that is actuated by a user to drive the needle into the injection site and deliver a dose of medicament. For example, in EP-B-1715903, the delivery of medicament is actuated by sliding an outer housing relative to other components of the device towards the injection site. In other devices, a button is pressed to release stored energy and initiate delivery of the medicament.
In UK patent GB-B-2239180 (Glaxo Group Limited), a self-injecting device is described that has a trigger, a release mechanism and separate means, controlled by the release mechanism, to discharge medicament. The device has a body formed from two parts that are moveable with respect to one another. The discharge means are actuated by operation of the trigger and release mechanism, and movement of one part of the body relative to the other part.
The actuation means in prior art autoinjectors varies between devices and the choice of actuation means is usually based on technical considerations such as ease of operation. However, it is found that actuation means that are easy to operate are susceptible to accidental delivery of medicament which may be dangerous. To overcome this problem, some autoinjector devices incorporate safety catches or locks that prevent accidental actuation. In these devices, the safety catch must be disengaged before the device can be actuated using the usual actuation means. The disengaging of a safety catch or similar mechanism adds an extra step to the actuation process. The extra step may be complicated and unintuitive and may not allow for a sufficiently quick delivery of a dose of medicament in an emergency situation where the user may be panicked and/or suffering.